1. Field of the Invention
The present invention relates to an automatic power control circuit and, more particularly, to one preferably used as an automatic power output control circuit applied to a power amplifier configured to be capable of selecting a desired one of a plurality of power output levels.
2. Description of the Related Art
A conventional radio transceiver uses an automatic power output control circuit (APC (Automatic Power Control) circuit) to keep power radiated from an antenna at the time of transmission constant. The APC circuit controls the intensity of radio waves radiated from the antenna by finely adjusting the gain of a high-frequency power amplifier in an RF (Radio Frequency) circuit section of the radio transceiver (see, e.g., Japanese Patent Laid-Open No. 2002-94392 and Japanese Patent Laid-Open No. 2002-280853).
Some of recent radio transceivers such as a transmitter system are capable of selecting a desired one of a plurality of transmission power output levels and performing communication. However, in each of conventional techniques including those of Japanese Patent Laid-Open No. 2002-94392 and Japanese Patent Laid-Open No. 2002-280853, an APC loop gain is kept constant regardless of power output level.